By Whitney Cranshaw, Colorado State University Cooperative Extension,
Specialist in Entomology

A family of insects (Sphingidae), when in the caterpillar stage, is known as hornworms.
About two dozen species of hornworms are found in Colorado. Although all feed
on leaves of various plants, most are innocuous, attracting little attention and causing
little, if any, injury to garden plants. Tomato and tobacco hornworms, which feed on
tomatoes and a few related plants, are an exception, being true garden pests.

Adults of all hornworms turn into large moths, known as "sphinx" or
"hawk" moths. Most fly at might and are rarely seen. A few species,
however, fly during cloudy afternoons and at dusk when they feed at flowers in a manner
similar to that of a hummingbird.